1. Field of the Invention
The present invention relates to active-matrix devices included in display apparatuses, electron-emitting apparatuses, light-emitting apparatuses, and the like.
2. Description of the Related Art
Active-matrix display devices having a matrix of pixels, each pixel including a display element and a driving circuit, often are used in liquid-crystal display apparatuses, electroluminescent (EL) display apparatuses, and the like.
The driving circuits (also referred to as “pixel circuits”) provided for the pixels of the active-matrix display devices have a function of retaining currents or voltages supplied via signal lines according to display signals and a function of supplying the currents or the voltages to the display elements. Pixel circuits in an EL display apparatus disclosed in Japanese Patent Laid-Open No. 2004-151166 have a function of examining the individual operations thereof by detecting values of currents passing through driving thin-film transistors (TFTs) thereof in addition to functions of setting driving currents and supplying the driving currents to EL elements. These three functions are switched using two control lines disposed in a transverse direction.
Pixel circuits in an organic EL display apparatus disclosed in U.S. Pat. No. 6,509,690 have a function of controlling emission time of EL elements using switches that block current paths connected to the EL elements in addition to a function of acquiring and retaining display signals and a function of supplying voltages or currents corresponding to the display signals to the EL elements. These functions can also be switched using two control lines. Japanese Patent Laid-Open No. 2004-325940 also discloses EL driving circuits capable of controlling the emission time.
The above-described pixel circuits have three of the four functions of acquiring and retaining signals, supplying currents or voltages corresponding to the signals to display elements, examining the operations of the pixel circuits, and controlling emission time of the display elements. All these four functions are required for the pixel circuits since all of them are important functions for display apparatuses and are important as testing techniques during the manufacturing process.
On the other hand, the number of control lines used for switching the functions needs to be minimized. In general, the number of pixels of display apparatuses needs to be increased to provide higher definition, and in particular, an increase in the number of rows of small display apparatuses is required. To this end, the areas of pixels need to be reduced, and in addition, the number of control lines needs to be minimized. Since pixel circuits include circuit components such as TFTs and capacitors and wiring lines connecting these circuit components disposed on a substrate, the areas of the pixel circuits are mostly determined according to circuit design rules. The control lines are wiring lines extending in the transverse direction in each row for selecting rows and switching functions of the pixel circuits in the rows. The control lines extend uninterruptedly regardless of difference in level, and have a certain limited width for reducing the resistance to a predetermined level. An increase in the number of control lines can lead to an increase in the pitch of the pixels, and can be unsuitable for high-definition display apparatuses.